1. Field of the Invention
The present invention relates to solid propellant disposal and recovery and more particularly, to a method of recovering aluminum from the waste propellant.
2. Description of the Prior Art
There is a considerable amount of waste propellant produced during the manufacture of solid propellant rocket motors, such as from the excess cast into the motor casing to compensate for shrinkage, from motors or masterbatches that do no meet specifications, as well as overage motors removed from service. Typically this waste propellant has been scrapped since the flammability and rubbery characteristics have been believed to prevent economical reclamation.
Large quantities of waste propellant have been and are now being burned in open burning pits. Due to increasing environmental pressure, many propellant producers are either now burning waste propellant and scrubbing the combustion gases or are planning on or will be required to do so in the future.
The expected quantity of waste composite propellant from the U. S. Space Shuttle Solid Rocket Motor boosters from 1976 through 1989 is expected to be about 8.times.10.sup.6 lbs. The cost of burning waste propellant is considerable. Economic recovery of propellant ingredients would save energy, cost, reduce materials and eliminate the costly, undesirable and hazardous open burning or incineration procedure.
A number of studies have been made on the recovery of aluminum from propellants as a part of a procedure in disposing of excessed propellant in a more ecologically acceptable manner than that of open pit burning. The approach of the various methods has been to depolymerize, or hydrolyze, the binder directly in the presence of all the propellant ingredients. A large number of catalysts and solvents have been tested, some of which resulted in very limited success. The results have been a partial breakdown of the binder system that allowed the recovery of only a small part of the aluminum present in an impure or contaminated state. A major portion of the aluminum was observed to remain with sufficient binder to result in a rubbery mass when dried.
Due to the expense of the reaction techniques, the exotic solvents required, and other problems encountered such as the recovery of impure materials and often the loss of much of the aluminum in the chemical reactions, the methods of propellant disposal have remained that of a burning process whereby any recovery value of oxidizer, fuel, i.e., aluminum and binder, are lost. Up to the present time, over six million dollars have been invested at Edwards AFB in a facility to burn propellants in a controlled and environmentally acceptable manner. Also, when ammonium perchlorate is present, the wet combustion process used results in a very corrosive solution, necessitating the use of titanium, tantalum-clad, or refractory-lined reactors. The effluents require neutralization, filtration, and the water soluble materials concentrated by reverse osmosis and ion exchange before the water can be disposed of or reused.